Ch. 28

Advantages of EDM

-Applicable to all materials that are fairly good electrical conductors -Hardness, toughness, or brittleness of material imposes no limitations -Fragile and delicate parts, complex geometries

Abrasive Waterjet Cutting (AWC)

-Can cut hard materials -Abrasives added to a Waterjet to improve efficiency

Abrasive Jet Cutting (AJC)

-Can cut hard materials -Abrasives mixed in high velocity air stream at 1,000 ft/s

Ultrasonic

-Can cut hard materials (great for glass) -Abrasives mixed in a slurry, ultrasonic transducers provide the mechanical agitation to remove the material

Etch Factor (E)

-Describes the undercutting of the mask layer -E=undercut(u)/depth(d)

Anisotropy (A)

-Directionality of the cut -A=1/E=d/u

Disadvantages of ECM (5)

-Initial tooling can be expensive -Environmentally harmful by-products -Current densities tend to concentrate at sharp edges or features (causing extra material removal near corners) -Control of electrolyte flow can be difficult -Parts may have lower fatigue resistance

Functions of Dielectric Fluid

-Local spark conductor -Coolant -Global electrical insulation -Flushes away debris

Waterjet Cutting (WJC)

-Only cuts soft materials like leather, paper, etc. -Water at 60,000 psi and 3,000 ft/s erode the material -Does not rely on abrasive particles

Disadvantages of EDM

-Slow compared to conventional machining -Produces a hard recast surface -Surface may contain fine cracks caused by thermal stress -Fumes can be toxic -Tool wear

Thermal Deburring

-Thermochemical process -Used to remove burrs by exposing workpiece to hot corrosive gases for a short period of time

Plasma Arc Cutting (PAC)

-Uses a superheated stream of electrically ionized gases (plasma) to melt and remove material -Can be used on almost any conductive material and on exotic materials at high rates

Advantages of ECM (4)

-Well suited for machining of complex 2D shapes -Delicate parts may be made (non contact) -Poorly machinable materials may be processed (including very strong, brittle, or tough materials) -Little to no tool wear

Wire EDM -----> ?????

2D

Sinker EDM ------> ?????

3D

Advantages of NTM (5)

Capable of making complex, delicate, and very small features Tight tolerances Often very good surface finish Little to no burring or residual stresses Materials with high strength or hardness can be machined

Common abrasive particle

Ceramics particles

Four basic groups of material removal using NTM processes

Chemical Etlectrochemical Thermal Mechanical

Methods to make a masking layer

Cut-and-peel Scribe-and-peel Screen Printing Photopatterning

In EDM, what fills the gap?

Dielectric fluid which becomes locally ionized

Most widely used tool electrode

Graphite

How do defects in etching occur?

If baths are not agitate properly

Advantages of CMP

Induces no stress or cold working in the workpiece Can be applied to almost any material Large areas can be etched simultaneously Virtually unlimited shapes Possible to make thin sections and very small fractures

Material Removal Rate Equation (MRR)

MRR=(Constant[C]*Current[I])/(Melting Temp.[Tm])

Chemical Machining Process (CMP)

Material is removed from a workpiece by exposing it to a chemical etchant

Nontraditional Machining (NTM) Processes

Material removal using something other than mechanical cutting/scraping

What materials allow Thermal Deburring to be most effective?

Materials of low thermal conductivity

Most important aspect of electrode (tool) material

Melting temperature

Convential End Milling vs. NTM

NTM typically have lower feed rate and require more power consumption NTM are usually slower and more expensive The feed rate in NTM is often independent of the material being processed Some NTM processes can machine the entire surface at once

Electrochemical Machining Process (ECM)

Removes material by anodic dissolution with a rapidly flowing electrolyte Chemical reaction dissolves workpiece but reaction only occurs locally in presence of electricity

Electrical Discharge Machining (EDM)

Removes metal by discharging electric current from a pulsating DC power supply across a thin interelectrode gap

Disadvantages of CMP

Requires handling of dangerous chemicals Disposal of potentially harmful byproducts Material removal rate is slow

Limitations in traditional machining processes:

Residual stresses and/or unwanted distortion of final part Burrs Delicate or complex geometries may be difficult or impossible High strength, high hardness materials are difficult to machine

Ion Beam Machining (IBM) or Focused Ion Beam (FIB)

Similar to EBM, uses a focused beam of charged ions (usually gallium) to remove material on the surface of a workpiece

In EDM, the electrodes are the ________

Tool and workpiece

When is EDM often used?

Tools and dies

True or False: Compared to other NTM processes, etch rates are slow

True

Four Major Forms of Free Abrasive Machining

Ultrasonic Waterjet Cutting Abrasive Waterjet Cutting Abrasive Jet Cutting

How CMP create patterns

Use gel milling thick gel is applied to workpieceonly in areas we want to etch Use a masking material

Electron Beam Machining (EBM)

Uses a beam of high-energy electrons focused on the workpiece to melt and vaporize a metal

Electrochemical Polishing

Uses a slower feed rate to produce a fine surface finish

Electrochemical Grinding

Uses an electrically-charged grinding wheel at low voltage; combination of electrochemical and mechanical material removal

Laser-Beam Machining (LBM)

Uses an intensely focused coherent stream of light to vaporize or chemically ablate materials

Typical expectations of NTM processes:

Very precise Apply very little to no force to the workpiece

Width of Final Geometry

W=(width in mask opening[w])+2*undercut[u]

Electrochemical Hole Machining

When this method is used to drill small holes; possible to achieve very high aspect ratios with this method

Friability

ability to break down into new, smaller particles

In ECM, the workpiece is the _____

anode

In ECM, the tool is the ______

cathode

the anode and cathode are separated by _______

electrolyte, which helps sweep away by-products of reaction

CMP is the common production method in _______

electronic circuit boards

Chemical reaction occurs everywhere the ______ contacts the workpiece

etchant

Masking material

selected areas are covered and the remaining surfaces are exposed to etchant